Particles are introduced into the center of the space surrounded by the hyperbolic electrode surfaces of a quadrupole ion trap mass spectrometer. Ions are desorbed or ablated from the surfaces of the particles with laser pulses from a Nd:YAG laser as the particles fall through the trap. The ions are trapped and subsequently mass analyzed using the mass-selective instability mode of operation of the ion trap. Desorption experiments were performed with approximately 100 [mu]m silicon carbide particles with an average of a few nanograms of adsorbed trimethylphenyl-ammonium chloride, tetraphenylphosphonium bromide, or 2,4,6-trinitrotoluene per particle. A conservative detection limit of 0.7 fm per particle was determined for tetraphenylphosphonium bromide. Ablation experiments were performed with approximately 50 [mu]m nickel particles for isotope ratio measurements with good agreement between accepted and average experimental values. 22 refs., 5 figs., 1 tab.